Measurement etch rate

The threshold fluence decreases with increasing dopant concentration and for the lowest concentration where ablation is observed (0.2% polyimide) the threshold fluence is about 0.7 J/cm2 at 248 nm and about 0.9 J/cm2 at 308 nm. Additionally, at fluences around 10 J/cm2, the maximum measured etching rates at 248 and 308 nm are about 3 and 6 pm/pulsc, respectively. While the etching rate for the 248 nm ablation of the 0.2% polyimide-doped sample has begun to saturate, the corresponding curve for the 308-nm ablation is still increasing. In comparison, the threshold fluence for the ablation of neat PTFE using 300 fs... 

Whether or not a chemical process step has been successful is difficult to measure, since there are few on-line measurable electrical properties. For example, film thickness and grain structure of polycrystalline silicon can be measured after a deposition step. However, their effect on device performance might not show up until subsequent doping or patterning steps fail. Similarly, it is possible to measure etch rates on-line by laser interferometry, but the etch profiles must be checked by electron microscopy. Unexpected mask undercutting or undiscovered etch residues can result in subsequent contact and device lifetime problems. 

W. Kem, A technique for measuring etch rates of dielectric films, RCA Rev. 557, December 1968. 

Fig. 3. a Measured etch rates as a function of natural logarithm fluence at high fluences (0.5 to 10 J cm-2), b Calculated etch rates of all polymers at 2,000 mj cm-2. REPRINTED WITH PERMISSION OF [Ref. 82], COPYRIGHT (2001) American Chemical Society... 

Fig. 73 Measured etch rates of TP vs the logarithm of the fluence (up to 600 mj crrT2) for different irradiation wavelengths. Insert shows the same plot for the complete linear fluence range. REPRINTED WITH PERMISSION OF [Ref. 221], COPYRIGHT (2002) Elsevier Science...

Doping of the siHcon can have a large effect on the etch rate, and layers of different materials such as Si02 and Si N can have different etch rates. Eor pressure sensors, thin diaphragms of Si or related materials are etched into the wafer (see Pressure measurements). 

The etch rates were measured by a surface profiler and field emission scatming electron microscopy (FESEM), and the etch profile were observed by FESEM. In this study, a C /Ar gas chemistry was chosen to obtain high etch selectivity of Si film to niobium oxide mask since CI2 gas was known to be a good etch gas for Si films. The etch rate, etch selectivity and etch profile of niobium oxide nanopillars and Si films were explored by varying the CI2 concentration, coil RF power and dc bias voltage to substrate. 

A Dektak siuface profilometer was used to measure the etch rates. The profiles of the etched films were observed by field emission scanning electron microscopy (FESEM). In addition, x-ray photoelectron spectroscopy PCPS) was utilized to examine the existence of possible etch products or redeposited materials, and to elucidate the etch mechanism of Co2MnSi magnetic films in a CVOa/Ar plasma. 

The 0 atom flow rate was measured by N02 titration as described elsewhere (21). At an 02 flow rate of 6.5 x 10-2 cm3 (STP)/s, reactor pressure of 73 Pa (0.55 torr) with the discharge off, and a power level of 15 W, the flow rate of 0 atoms was found to be 2.4 x 10-2 cm3 (STP)/s the latter figure represented an 18 conversion of 02 to 0 atoms. Assuming complete 0(3P)-induced oxidation of the polymer samples to C02 and H20, the flow rate of 0 atoms was at least eight times that required to maintain the highest etch rate observed (0.8 mg/cm2-h, in TB). 

Polymer sample temperature, measured with a thermocouple situated beneath a thin glass platform supporting the sample, depended on etch rate of the polymer the maximum temperature rise encountered in any run was 9 K, exhibited by TB after 20 min exposure to 0(3P). The... 

The 02 reactive ion etching rates of poly(disilanylenephenylene) 10 and 11, and polyimide (PIQ) were measured. As can be seen in Figure 4, the polymers 10 and 11 show very high etching resistance against the oxygen plasma, compared with the PIQ. 

The authors would like to thank Dr. B. Fay for resist exposures by ACO synchrotron radiation, Dr. P. Parrens from LETI (Grenoble) for measurement of plasma etching rates and the "Direction des Recherches, Etudes et Techniques" (DRET) which partly sponsored this work. 

To determine the number of equivalent Ti monolayers (1 equivalent Ti monolayer = 2 x 1015 Ti atoms/cm2) needed on the polymer surface to protect the underlying organic film during 02 RIE, several PMMA films were treated with TiCLt under different processing conditions. After treatment with TiCLt the films were etched in an 02 plasma for different lengths of time and the etching rates were determined. The Ti concentration in the samples was measured both before and after etching (Table II). 

Polymer Ti Concentration Measured by XFS (atoms/cm2 x 1(T15) Before Etching After Etching Rate 0 (A/min) ATi Upon Etching (%)... 

Refractive index measurements made by this technique are of sufficient accuracy to make this a valuable research tool in studying and characterizing the dry etch behavior of novel polymer resist materials. In situ etch rate can be measured and analyzed quickly without any prior knowledge of the polymer s physical properties. 

This leads to an efficient and non-destructive in situ etch rate measurement technique which does not require any prior knowledge of film properties. The analysis can also be used to semi-quantitatively gauge the degree of "roughening" imparted to a polymer film surface during RIE processing. 

We first experimented with the Quartz Crystal Microbalance (QCM) in order to measure the ablation rate in 1987 (12). The only technique used before was the stylus profilometer which revealed enough accuracy for etch rate of the order of 0.1 pm, but was unable to probe the region of the ablation threshold where the etch rate is expressed in a few A/pulse. Polymer surfaces are easily damaged by the probe tip and the meaning of these measurements are often questionable. Scanning electron microscopy (21) and more recently interferometry (22) were also used. The principle of the QCM was demonstrated in 1957 by Sauerbrey (22) and the technique was developed in thin film chemistiy. analytical and physical chemistry (24). The equipment used in this work is described in previous publications (25). When connected to an appropriate oscillating circuit, the basic vibration frequency (FQ) of the crystal is 5 MHz. When a film covers one of the electrodes, a negative shift <5F, proportional to its mass, is induced ... 

A very accurate measurement of Ccrjt would allow back-calculation of the surface energy for a given crystal. Because Ccrjt is dependent on the square of Y, such a measurement could be a very sensitive method of measuring interfacial energy at dislocation outcrops. The calculated interfacial energy from our experiments is 280+ 90 mJm- for the rhombohedral face of quartz at 300°C. Parks (10) estimated 25°C value of 360 + 30 mJm is well within the experimental error of our measurement. The best way to determine the value of Ccrjt would be to measure etch pit nucleation rate on... 

Several refinements of our experiments could test these theories further. By measuring etch pit densities as well as pit dimensions on sequentially-etched crystals, nucleation rate data and pit growth data could be collected, yielding information about the rate-limiting steps and mechanisms of dissolution. In addition, since the critical concentration is extremely dependent on surface energy of the crystal-water interface (Equation 4), careful measurement of Ccrit yields a precise measurement of Y. Our data indicates an interfacial energy of 280 + 90 mjm- for Arkansas quartz at 300°C, which compares well with Parks value of 360 mJm for 25°C (10). Similar experiments on other minerals could provide essential surface energy data. 

From a knowledge of the absorption coefficient aeff and the threshold fluence Fth, the value of the photochemical contribution to the etch rate, Fph0to> can calculated and subtracted from the measured hole depth for any given fluence. The difference, which according to this model is the thermal etch rate Fthermai will be modeled by Eq. (5) by rewriting it as... 

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